"One of the first messages you’ll see after logging into Windows 8 for the first time (aside from a message about activating Windows) is a request to “Trust this PC.” But why does Microsoft want you to “trust” your PC?

A trusted PC is a Microsoft account security feature. Only trusted PCs are allowed to synchronize passwords. You can also more easily reset your password from a trusted PC, should you ever forget it.

You should only trust private PCs, not public PCs that other people have access to. If you share a PC with other people, anyone with access can reset your Microsoft account password from that PC."